1. Field of the Invention
The present invention relates to pushbutton switch mechanisms. In particular, the present invention relates to a pushbutton switch mechanism which is capable of either momentary or alternate action operation by selective removal or insertion of a removable alternate action stop member.
2. Description of the Prior Art
There are various constructions of pushbutton switches known in the prior art. One typical type of pushbutton switch has a housing and an elongated slider or plunger which moves in a longitudinal axis within the housing. The slider normally carries a plurality of conductive contacts which are brought into engagement with terminals carried by the housing. The particular terminals which are connected by the conductive contacts depend upon the position of the slider with respect to the housing. The slider is normally biased outwardly from the housing by a helical compression return spring.
One type of pushbutton switch which has found wide use in the past is a miniature pushbutton switch which is usable with various types of electronic circuitry. These types of switches have found particularly wide use in radio and television receivers and test instrumentation.
There are three typical operating modes of miniature pushbutton switches. The first mode is referred to as "alternate action" or "push to make/push to break". In this operating mode, the slider has two stable switch positions. Depressing the pushbutton causes the slider to move from one stable position to the other.
The second typical operating mode is the "momentary" mode. In this mode of operation, the slider is biased by the helical return spring so that it always returns to the same position after force is released from the pushbutton head.
The third operating mode is the "interlocking" mode. In this mode, several momentary pushbutton switches are mounted side-by-side in a common chassis. A sliding interlock release bar moves in the chassis so that only one switch is depressed at any time. An example of this type of interlocking arrangement is shown in U.S. Pat. No. 3,722,313 by Schadow.
The typical arrangement for achieving alternate action operation of a miniature pushbutton switch includes a heart-shaped cam groove or surface and some form of pin, ball or detent which rides in the heart-shaped cam groove to position and stop the slider at one of the two stable positions defined by the heart-shaped cam groove. Various configurations of this basic arrangement have been used in the past, as shown by the following patents:
______________________________________ U.S. Pat. No. Re.27,963 Schadow 1,309,840 Bramming 1,323,822 Bramming 2,671,354 Goos 2,946,237 Hebert 2,956,446 Ensign, Jr. et al 2,996,593 McMains 3,229,548 DeRougemont et al 3,406,589 Gaber 3,411,376 Weber et al 3,436,983 Krantz 3,493,705 Noll et al 3,566,705 Frydman 3,639,714 Fujimoto et al Japanese Utility Model 12,334/68 Japanese Patent Application 43-23497 Japanese Patent Application 50-26914 French Patent 1,250,589 French Patent 1,285,260 French Patent 1,367,668 French Patent 2,373,863 French Patent 2,326,773 United Kingdom Patent 958,663 United Kingdom Patent 1,494,334 United Kingdom Patent 1,503,916 United Kingdom Patent 1,164,260 German Patent 1,233,456 German Patent 1,260,586 German Patent 1,295,048 German Gebrauschsmuster 1,915,584 ______________________________________
In recent years, the configuration which has found widest use in miniature pushbutton switches is that shown in U.S. Reissue Patent No. 27,963 by Schadow. In this configuration, the stop member is in the form of a U-shaped pin. One leg of the pin is used as a detent and rides in the heart-shaped cam surface. The other leg is used as a pivot to allow the detent leg to move in a direction which is transverse to the movement of the slider so as to follow the shape of the cam surface. The U-shaped pin is positioned so that a portion of a helical return spring surrounds the U-shaped pin and engages the crosspiece of the pin to retain the pin in place. To convert the switch to momentary action, the helical spring is compressed and the U-shaped pin is lifted out. The helical spring can then be released, and the switch is capable of use either as a momentary switch, or as one of a group of switches in an interlocking configuration.
The arrangement shown in the Schadow Reissue Pat. No. 27,963 has the advantage of providing rapid conversion between alternate action and momentary operation, so that the manufacturer can use the same switch configuration and can convert existing inventories of momentary switches to alternate action switches or vice versa by the insertion or removal of the U-shaped pin. In addition, the use of the helical spring to surround and hold the U-shaped pin in place minimizes the number of parts needed to hold the U-shaped pin in position. In comparison, other configurations such as that shown in the DeRougemont Pat. No. 3,229,548 and in German Pat. No. 1,233,456 have required a separate retainer to hold the stop pin in place. This retainer is an unnecessary part which performs no function if the switch is used in a momentary mode of operation.
The configuration shown in the Schadow Reissue Pat. No. 27,963 does, however, have some shortcomings. In particular, the proper operation of the switch is dependent upon the orientation of the helical spring. If the end of the helical spring abuts the side of the cross member of the U-shaped pin, it can limit the side-to-side swinging movement of the U-shaped pin and cause failure of operation of the switch. Care must be taken, therefore, to ensure that the end of the helical spring does not contact the side of the U-shaped pin.
In addition, the configuration shown in the Schadow Reissue Pat. No. 27,963 exposes a substantial portion of the U-shaped pin, since most of the pin is located above the top surface of the cover (or "terminal board") of the switch housing. Thus the U-shaped pin can be damaged during manufacture of the switch itself, or during construction of a switch assembly in a chassis by the customer.
There is a continuing need for an improved pushbutton switch which is capable of rapid and simple conversion between an alternate action mode of operation and a momentary or interlocking mode of operation. In particular, there is a need for a pushbutton switch configuration which differs from and avoids the shortcomings of the configuration shown in the Schadow Reissue Pat. No. 27,973, yet utilizes a minimum amount of parts to provide the alternate action operation.